# Cross-Chain Value Transfer
This section will explain how to enable ERC-20 value transfer between Baobab network and your ServiceChain with the provided test code. You will add KLAY to the operator account and deploy bridge and ERC-20 contracts. Then you will register the contract address on SCN. And you will test an ERC-20 value transferring.
### Prerequisites
* We assume that you installed the ServiceChain, and connected the ServiceChain to the Baobab EN by the instructions in [Connecting to Baobab](https://archive-docs.klaytn.foundation/content/installation-guide/deployment/service-chain/getting-started/en-scn-connection).
* Clone the repository [servicechain-value-transfer-examples](https://github.com/klaytn/servicechain-value-transfer-examples).
* Install `Node.js` (v14) and `npm` ([How to install](https://nodejs.org/en/download/package-manager/))
* This example leverages two packages, axios and caver-js, which both support v14.
### ERC-20 Token Transfer (one-step)
#### Step 1: Add KLAY to the operator accounts.
Connect to the SCN and check the account addresses by executing `subbridge.parentOperator` and `subbridge.childOperator`.
```
$ kscn attach --datadir ~/data
> subbridge.childOperator
"0x10221f7f9355017cd0c11444e7eecb99621bacce"
> subbridge.parentOperator
"0x3ce216beeafc62d20547376396e89528e1d778ca"
```
`subbridge.parentOperator` and `subbridge.childOperator` must have enough KLAY to send a transaction. Note that `subbridge.parentOperator` is an account on the Baobab network, and `subbridge.childOperator` is an account on the ServiceChain network. Create a test account on a [Baobab Wallet](https://baobab.wallet.klaytn.foundation/) and get test KLAY from the faucet. Then send some KLAY to the `parentOperator`. `childOperator` has to get KLAY from the test account generated by `homi` ([Refer to EN Setup and SCN Connection Guide](https://archive-docs.klaytn.foundation/content/installation-guide/deployment/service-chain/getting-started/en-scn-connection)).
```
$ kscn account import ~/homi-output/keys_test/testkey1
Your new account is locked with a password. Please give a password. Do not forget this password.
Passphrase:
Repeat passphrase:
Address: {80119c31cdae67c42c8296929bb4f89b2a52cec4}
```
```
$ kscn attach --datadir ~/data
> personal.unlockAccount("80119c31cdae67c42c8296929bb4f89b2a52cec4")
Unlock account 80119c31cdae67c42c8296929bb4f89b2a52cec4
Passphrase:
True
> klay.sendTransaction({from:"80119c31cdae67c42c8296929bb4f89b2a52cec4", to:subbridge.childOperator, value: web3.toPeb(1000, "KLAY")})
"0x84caab84ebf0c4bb4ecf0a7849f1de3e479f1863a95f70c51047a7ca7bc64b33"
```
Check if the operator accounts have enough balance. You can query from the console of the SCN node where the subbridge is installed as follows:
```
> klay.getBalance(subbridge.childOperator)
1e+21
> subbridge.childOperatorBalance
1e+21
> subbridge.parentOperatorBalance
1e+18
```
#### Step 2: Deploy Contracts
* Connect to the SCN and prepare the node environment for contract deployment. Clone the repository [servicechain-value-transfer-examples](https://github.com/klaytn/servicechain-value-transfer-examples).
In this step, we would deploy both the bridge contract and token contract in the parent as well as the child chain. Token contracts are for mint/transfer test and bridge contracts are used to listen/handle value transfer requests.
```bash
$ git clone https://github.com/klaytn/servicechain-value-transfer-examples
$ cd servicechain-value-transfer-examples
$ npm install
$ cd erc20
```
On a text editor, edit the `bridge_info.json` as below.
* Replace `url` in the `child` section (SCN node on ServiceChain network) with your SCN node IP and the proper port number from `RPC_PORT` in `kscnd.conf`.
* Replace `child.key` with `testkey1` that was generated by `homi`.
* Set `child.operator` to the `subbridge.childOperator` address that we examined in the previous step.
* Replace `url` in the `parent` section (EN node on Baobab network) with your EN node IP and the proper port number from `RPC_PORT` in `kend.conf`.
* Replace `parent.key` with the private key of the test account created from [Baobab Wallet](https://baobab.wallet.klaytn.foundation/) in the previous step.
* Set `parent.operator` as the `subbridge.parentOperator` of the previous step.
```
{
"child" : {
"url": "http://192.168.0.1:7551",
"key": "0x66cb283353589a10866b58d388e9d956e5a9c873a8c78fa4411d460c19c494ea",
"operator": "0x10221f7f9355017cd0c11444e7eecb99621bacce"
},
"parent" : {
"url": "http://192.168.0.5:8551",
"key": "0x26f4b5ac42ceabcfd3b23a991fdbfc792d10ce700a99582fdf9185a8f163b790",
"operator": "0x3ce216beeafc62d20547376396e89528e1d778ca"
}
}
```
Perform the token deployment by running the command `node erc20-deploy.js`. This script deploys both the bridge contract and the token contract, and it outputs API usage to initialize bridge pair.
```
$ node erc20-deploy.js
------------------------- erc20-deploy START -------------------------
> info.bridge: 0xEa024d8101E112330f2d7B1a7e7932034E206721
> info.token: 0xbE641028610F628835C36F12bE62d54d74308D70
> info.bridge: 0xA5af6Ffe13b367626B5AdF827DdE7438E3Db4463
> info.token: 0x52F8Fa79Fa6D37b18b7AC8f9Ca835373f3C9270f
> subbridge.registerBridge("0xEa024d8101E112330f2d7B1a7e7932034E206721", "0xA5af6Ffe13b367626B5AdF827DdE7438E3Db4463")
> subbridge.subscribeBridge("0xEa024d8101E112330f2d7B1a7e7932034E206721", "0xA5af6Ffe13b367626B5AdF827DdE7438E3Db4463")
> subbridge.registerToken("0xEa024d8101E112330f2d7B1a7e7932034E206721", "0xA5af6Ffe13b367626B5AdF827DdE7438E3Db4463", "0xbE641028610F628835C36F12bE62d54d74308D70", "0x52F8Fa79Fa6D37b18b7AC8f9Ca835373f3C9270f")
------------------------- erc20-deploy END -------------------------
```
#### Step 3: Token transfer
Perform token transfer with the command `node erc20-transfer-1step.js`. This one-step token transfer requires modification of an ERC-20 token implementation. If you don't want to modify the token contract or you have a token contract that is already deployed, please refer to [ERC-20 Token Transfer (two-step)](#erc-20-token-transfer-twostep).
```
$ node erc20-transfer-1step.js
------------------------- erc20-transfer-1step START -------------------------
alice balance: 0
requestValueTransfer..
alice balance: 100
------------------------- erc20-transfer-1step END -------------------------
```
If the result is `alice balance: 100`, then it has been executed successfully.
### ERC-20 Token Transfer (two-step)
Run erc20-transfer-2step.js for the two-step transfer example. With this two-step token transfer example, unmodified ERC-20 token contracts can be used. The two-step transfer consists of two function calls: (1) approve the bridge contract first, and then (2) call the contract function `requestERC20Transfer()`. We do not deploy contracts in this section since we already deployed both bridge and token contracts. You must deploy first if you didn't deploy them. You can deploy the contract using `node erc20-deploy.js`.
```
$ node erc20-transfer-2step.js
> ------------------------- erc20-transfer-2step START -------------------------
> alice balance: 100
> requestValueTransfer..
> alice balance: 200
------------------------- erc20-transfer-2step END -------------------------
```
### KIP-7 Token Transfer via ERC-20 Interface (two-step)
[KIP-7](https://kips.klaytn.foundation/KIPs/kip-7) is a token standard compatible with ERC-20. We can call `requestERC20Transfer()` function to a KIP-7 token contract to transfer KIP-7 tokens between a parent chain and a child chain. In the case of sending KIP-7 tokens via the ERC-20 interface, we call the `approve()` function to allow the bridge to send the tokens on behalf of the transaction sender. Then call the `requestERC20Transfer()` function. The below command deploys the bridge contract and a KIP-7 contract.
```
$ node kip7-deploy.js
> ------------------------- kip7-deploy START -------------------------
> info.bridge: 0x04e929Cd2A08acd28a210369407D8Ca237Edd8FE
> info.token: 0xE0E2fC6C7d1eB069153E0c12a4C87B01586b39e7
> info.bridge: 0xEb502159A4B4E876B1cb423f250DCC0d276e01b6
> info.token: 0xd4f02Ca1d49674056A9ec78fbBDc9e1e97726A4F
> subbridge.registerBridge("0x04e929Cd2A08acd28a210369407D8Ca237Edd8FE", "0xEb502159A4B4E876B1cb423f250DCC0d276e01b6")
> subbridge.subscribeBridge("0x04e929Cd2A08acd28a210369407D8Ca237Edd8FE", "0xEb502159A4B4E876B1cb423f250DCC0d276e01b6")
> subbridge.registerToken("0x04e929Cd2A08acd28a210369407D8Ca237Edd8FE", "0xEb502159A4B4E876B1cb423f250DCC0d276e01b6", "0xE0E2fC6C7d1eB069153E0c12a4C87B01586b39e7", "0xd4f02Ca1d49674056A9ec78fbBDc9e1e97726A4F")
------------------------- kip7-deploy END -------------------------
```
The below command is an example of sending KIP-7 tokens using the ERC-20 interface with `requestERC20Transfer()`.
```
$ node kip7-transfer-2step-erc20-interface.js
> ------------------------- kip7-transfer-2step-erc20-interface START -------------------------
> alice balance: 0
> requestValueTransfer..
> alice balance: 100
> ------------------------- kip7-transfer-2step-erc20-interface END -------------------------
```
Please refer [service-chain-value-transfer-example](https://github.com/klaytn/servicechain-value-transfer-examples) for the other cases.
### Native Support for KIP-7 and KIP-17 (To Be Implemented)
Currently, the bridge contract provided by the Klaytn team supports only `requestERC20Transfer()` and `requestERC721Transfer()` for token transfer. The corresponding request functions for KIP-7 and KIP-17 will be supported soon. Before the implementation is done, as you can see above, you can transfer KIP-7 tokens using ERC-20 interfaces.
### Value Transfer for ERC-721, KIP-17, and KLAY
The workflow for ERC-721, KIP-17, and KLAY is the same as above. [`erc721`](https://github.com/klaytn/servicechain-value-transfer-examples/tree/main/erc721), [`kip17`](https://github.com/klaytn/servicechain-value-transfer-examples/tree/main/kip17), and [`klay`](https://github.com/klaytn/servicechain-value-transfer-examples/tree/main/klay) directories contain corresponding example source code.